The present invention relates to a roll of a polyvinyl alcohol film wherein a very long polyvinyl alcohol film can be rolled up and the rolled up film has an excellent appearance, and a polarizing film having an excellent polarizing property prepared from the film roll.
Polyvinyl alcohol films have been generally prepared by dissolving a polyvinyl alcohol resin in a solvent, deaerating the resulting solution, forming it into a film by a solution casting method and drying the film by using a metallic heating roll and the like. The film which has passed through the above drying step is then dried by a drier to evaporate the moisture contained in the film, provided again with a predetermined amount of moisture in a humidity conditioner and rolled up around a cylindrical core tube to give a rolled up film to be put on the market. The thus rolled up polyvinyl alcohol films have been utilized for many applications as a film having an excellent shape stability. One of the useful applications is an optical film, particularly a polarizing film.
However, when rolling up a polyvinyl alcohol film around a cylindrical core, problems may arise in appearance of the film, e.g., generation of wrinkles and folds. Therefore, careful process step management is required. If such problems arise, another problem of course arises. For example, if a polarizing film is produced from a film that has once caused such a problem, the polarizing property is deteriorated.
It is an object of the present invention to provide a roll of a polyvinyl alcohol film having an excellent appearance and accordingly having an optical homogeneity with industrial advantage and without requiring severe process management as conventionally required.
A further object of the present invention is to provide a roll of a long polyvinyl alcohol film from which a polyvinyl alcohol film having an excellent appearance and an optical homogeneity is obtained when unwound.
Another object of the present invention is to provide a polarizing film having an excellent polarizing property.
These and other objects of the present invention will become apparent from the description hereinafter.